Toward empirical evaluation of left ventricle function: A novel mathematical mapping

A strategy is developed to facilitate quantitative analysis of left ventricle morphology based on clinically measured surface geometry and muscle fiber patterns rather than lower order geometric approximations previously required. A transfer function is derived which maps measured three-dimensional ventricle surfaces and associated muscle fiber patterns to a right circular cylinder, while preserving characteristic kinematics of the system. Functional analysis of ventricular morphology at various stages of the cardiac cycle proceeds by using classical methods on the cylindrical ventricle model, with substantially reduced analytical complexity when compared to similar calculations on the real ventricle shape. Functional morphology of the real ventricle shape at any stage of the cardiac cycle is subsequently deduced by applying the inverse of the transfer function in order to map the computed right circular cylinder back to its corresponding real ventricle shape. Limitations of the method are discussed in the context of real left ventricle performance, and extension of the method for analysis of functional morphology in other biomechanical systems is explored

Transport and stirring induced by vortex formation

The purpose of this study is to analyse the transport and stirring of fluid that occurs owing to the formation and growth of a laminar vortex ring. Experimental data was collected upstream and downstream of the exit plane of a piston-cylinder apparatus by particle-image velocimetry. This data was used to compute Lagrangian coherent structures to demonstrate how fluid is advected during the transient process of vortex ring formation. Similar computations were performed from computational fluid dynamics (CFD) data, which showed qualitative agreement with the experimental results, although the CFD data provides better resolution in the boundary layer of the cylinder. A parametric study is performed to demonstrate how varying the piston-stroke length-to-diameter ratio affects fluid entrainment during formation. Additionally, we study how regions of fluid are stirred together during vortex formation to help establish a quantitative understanding of the role of vortical flows in mixing. We show that identification of the flow geometry during vortex formation can aid in the determination of efficient stirring. We compare this framework with a traditional stirring metric and show that the framework presented in this paper is better suited for understanding stirring/mixing in transient flow problems. A movie is available with the online version of the paper

A Novel Technique for Free-Surface Elevation Mapping

Recently, there has been an increased interest in the interaction of vortices and turbulence with free surfaces. A central issue in understanding the free surface turbulence is to relate the surface elevation to the near-surface flow field. In that respect, the lack of a global surface mapping technique which could reveal the temporal evolution of the surface elevation has prevented the progress of viable research. Therefore, in this abstract we present a new technique, integrating optics, colorimetry, and digital image processing, to measure the three-dimensional surface elevation for a time-evolving flow. The basic idea is to color code the surface slopes by light beams of different colors. This is achieved by first using a diffused white light source to illuminate a specially designed color palette

Observations of large-scale fluid transport by laser-guided plankton aggregations

Diel vertical migration of plankton has been proposed to affect global ocean circulation to a degree comparable to winds and tides. This biomixing process has never been directly observed, however, due to the inability to predict its occurrence in situ or to reproduce it in a laboratory setting. Furthermore, it has been argued that the energy imparted to the ocean by plankton migrations occurs at the scale of individual organisms, which is too small to impact ocean mixing. We describe the development of a multi-laser guidance system that leverages the phototactic abilities of plankton to achieve controllable vertical migrations concurrently with laser velocimetry of the surrounding flow. Measurements in unstratified fluid show that the hydrodynamic interactions between neighboring swimmers establish an alternate energy transfer route from the small scales of individually migrating plankton to significantly larger scales. Observations of laser-induced vertical migrations of Artemia salina reveal the appearance of a downward jet, which triggers a Kelvin-Helmholtz instability that results in the generation of eddy-like structures with characteristic length scales much larger than the organisms. The measured energy spectrum is consistent with these findings and indicates energy input at large scales, despite the small individual size of the organisms. These results motivate the study of biomixing in the presence of stratification to assess the contribution of migrating zooplankton to local and global ocean dynamics. The laser control methodology developed here enables systematic study of the relevant processes